Roger Federer progressed to the Swiss Indoor semfinals in his hometown of Basel after compatriot Stanislas Wawrinka was unfit to play their scheduled quarterfinal clash on Thursday.
Wawrinka, who finished runner-up to Andy Murray last week at the European Open as the Scot won his first singles title since returning from hip resurfacing surgery, cited a back issue as the reason for his withdrawal.
The 34-year-old overcame Frances Tiafoe in three sets in two hours and 32 minutes in the previous round.
Top seed Federer, 38, will face either No. 3 seed Stefanos Tsitsipas or Filip Krajinovic in the final four.
The 20-time Grand Slam champion is the most successful player in the history of the Swiss Indoors, having won nine titles at the tournament where he was a ball boy as a youngster.